This invention relates to a structure of a flexible membraneous weir, and more particularly to a flexible membraneous weir for which a V-deformation starts in a predetermined portion at one stage of its collapsing process.
Generally, an air type flexible membraneous weir disposed across a river is erected by charging air therein and collapsed by discharging air therefrom. Contrary to a water type flexible membraneous weir which is erected by charging water therein and collapsed by discharging water therefrom, with regard to the air type membraneous weir, if air once filled therein is discharged in order to collapse it, its membrane wall starts deforming in the shape of a letter "V" at one portion or two in the river width direction at a time when the internal pressure is decreased to such an extent as to make its weir height to be about 70% of the initial weir height (a V-notch phenomenon). The result is a concentration of the stream into said V-notch portion. Furthermore, the portion where the V-notch phenomenon will occur is not certain, since it depends on various factors such as a geographical form of a river, a state of a stream, differences of workmanship of a flexible membraneous weir and the like. Therefore, there is a possiblity that said V-notch phenomenon will occur in the vicinity of the surfaces of the river walls and that the flow concentrates on this portion. As a result, the river wall at the down stream side will be excavated and the banks will be damaged. In order to prevent the foregoing, the river walls at the down stream side are required to be reinforced. Likewise, in order to be ready for concentration of the flowing at any places, protection bed for preventing the excavation is required to be constructed along the whole area in the river width direction which often results in high costs of the construction fees. The present invention was accomplished in view of the above.